there have been several instances where a new forum user such as yourself will come to the forum to buy liberty reserve, get into a trade, and then never deliver the bitcoins. because of a double spending race attack or finney attack, only after a bitcoin transaction has several confirmations should the liberty reserve be sent to you.

as a public service message:

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When you trade OTC you engage in a transaction with people you possibly know nothing about. You may send your BTC to the person, and never get anything back. Or you may send your $currency to the person expecting BTC, and get nothing in return. This is a highly undesirable outcome for you, and you should do your best to guard against that. If you do not have a history of previous transactions with this person, or otherwise do not trust your counterparty, there are several mechanisms you can use to mitigate the risk of fraud: